Aircraft landing system



Feb. 17, 1948. R. H. vARlAN AIRCRAFT LANDING SYSTEM s Sheets-sheetl Filed Jan. 29, 1944 INVENTOR RUSSELL lf lm/AN Feb,v 17, 1948. R. H. vARlAN AIRCRAFT LANDING SYSTEM 3 Sheets-Sheet 2 Filed Jan 29 1944 .N .mvg

Feb. 17, 1948. R, H, VARlAN AIRCRAFT LANDING SYSTEM Filed Jan. 29, 1944 5 Sheets-Sheet 5 Patented Feb. 17, 1948 Russell Htl Varian,` Garden City, N. Y., assignor to 'Iher-vSperry-f` Corporation; as.. corporation oi "Delawarev Application Janna-1:35.29, 1944. Seri'al No...520,207"

(CL: 25d-IDI This invention relatesto. radio landingsystems and:` particularly concerns transmittingl systems for projecting radio beams-to forma landing path alongthe intersection of the radio beams; Radio landing" systems... of thisjtype havelieretof'ore reduired one or more .antennas or4 radiators positioned` adjacent"` a runway,... or at one eudlthereof*` inamanner to form a path for landing' .planes .on a particular runway. These radiators .usually extend; several 'A feet above the ground and; must bearranged so theyj do not obstructthe landing path; the use of g aircraft; has progressed andgith number. ofjplanes .landingl.. at.. particular airports has. `increased;itlhfas. become necessary to` p rovdepara1lel'-runways arranged., so twoV or more planes, mayapproacli Vthe landing iield" atthe saine time andland'on separate runways. To proyide for simultaneously .landing several" aircraftgiat; the. same. landing eld' it is necessary to; have; apparatus for .dening separate; radio landing. paths for; each .015. the, several j. parallel runways. the numberv of... runways is, increased;` the. radiators must be arrangedso they do not obstruct `any ofthe parallel landing paths. be .accomli'shediby mening.u the anten-v nas further. away from' their.. selected. runways, but regardless oilllthe` .distance ,towhichthey are removecttney will. remain obstructions within the very. much y enlarged `area 'for parallel4 landing on adjacent.. runways. Furthermore, parallel landings;.-.rnust .be .possibleirom ,alidirections .so antennas surroundingia..landingarea form hazardsfthat endangenlanding craft...

The. maior.,objectof` the` present invention is toproyide a landing .path formed "by radio beams from radiators arrangedsubstantially flush with the ground. so theyido not.form obstructions. in any direction.

Another. obj ect vofi the, .present ...invention is to provide. .a .plurality of .parallel landing paths for a.. plurality oparallelLrunways so planesmay follow` the individual.' landing paths. to .landV on the. various... runways simultaneously...

. Aiurtheri-obiect of.` the lpresent ,invention .is .to provide a landing path formed bytheintersection ,or a. pair., ot. `conicallyfshap ed..beamsoi electromagnetic..energy,

4A iurther object otthe` presentiinventionis toproyid'e.aflandi11g;path .formed Abyeradio,beams from., cone-nre. radiating--wave guides. arranged sulcstantiallyifluslfn withthe surace .oi ,the landing area.

. .Aifurther object-.oithe` present inventionis to .providea landing path. denedby vthieintersection ot-two eonicallyrshaped lequi-signal. surfaces.. nach of which..is;form.ed Vbetween apair. of..conical1y shaped..radiov beams emitted .from conefre. .radlat ingsystemsr g I lA;Stille-mller..obect,iofthelnvention to provide an' equi-signal surface between Ytwo coni# cally-shaped iradio-beams^ from a pair of I radiatingwave` guidesconnected tothe same trans Initte1-,-V thewave guides -being constructed' to profvid`e= differentfphas ey velocities for energy supplied i from the'transmitter.-

having a plurality of parallel' runways extend'- ing'irrevarious directions and' showing landing paths i for each f ofv saidv runways formed by*y the intersectionof conically-shaped' equi-signal sur'- J faces;

' Figa 2-is a -plan-viewfof one oFthelanding-strips included: in Fig-. 1, Vshowing a sectional representation of* the various radioi beams#A which: are emitted by transmitting systems to formi the-*two equi-signalsurfaces that intersect to'id'ene'the landing path;

Fig. 3e isA af Vvertical sectionY taken along the axisson one ofthe equi-signal surfaces shownin Fig. 2: Y

Fig: 4 is a; sectenal-viewof theradio beams taken alongtlle'llne `l--tlof Fig.l 2';

Fig. 5 is a rear elevation looking outwardly alongftl'ie*equi-signal surfaces shown ink Fig-.- 2;

Fig. Gis-- an enlarged perspective illustration of ther conically-shaped equi-signal surface forming one of the landing pathsfshown in Fig.v I;

Fig. 'iA is aschematic `diagram ofi a=- preferred transmitting system showing one4 arrangement of thev radiators for de'ning a landing; path selectively` from opposite ends ofla runway Fig: 8 is arr enlarged perspective.: View offone ofthe` radiating wave-'guides shownsA inFig: 'I with portion-s broken away for thepurposesxof clearness;

Fig: 9 is a vertical'section of the wave guide radiator-takenV on theV line Q-Sfof Fig. '7;

Fig.` loris a vertical section of the'wave'guide radiators taken`on the line `llT-I 0` of 'Figa 7';

Fig.l 111 is a Verticall section showing: one =ar rangement formounting a wave guide, sucli` as shown" inv Fig. 8,y substantially :flushv with: the surface ofi the landing area; and"v Fig. 12'is a schematic diagram-of receiver apparatus which*v may be-v usedV on an aircraft to follow a-flandingpath defined according toethe invention. According tothe invention inv its preferred form,A eachof the'landing'paths for a plurality of`landing strips is formed by the intersection of "apair of conically-shaped equi-signal Vsurfaces `ofpelectrornagnetic energy. Each of theseiconi- Ycally shaped equi-signal surfaces isv formedfbetween. aA pairl of conically-shaped radio beams emittedfrom cone-fire wave guide radiating-sys!- tems constructed such that said beams are arranged in nested relation. The cone-fire Wave guide radiators are supported substantially flush with the surface of a landing area and project beams upwardly from a point along the landing area which approximately coincides with the contact point at which approaching aircraft land on the runway.

Fig. 1 shows a landing area, 2| as it may appear to an observer in an aircraft approaching to land thereon. Tlis landing area is shown ashaving a set of three parallel runways 22, 23 and 24 extending in one direction and a second set of three parallel runways 25, 26 and 21 extending in a-direction normal to the other set of runways. In order that landing paths may be formed for approaching each of the runways from either direction, a pair of radiating systems together with appropriate transmitting apparatus isprovided for each end of eachofthe runways and may be vcontrolled from a control tower 29.l `As shown in Fig. 1, the runways 22.23-and- 24 are in use and are to be approached from the direction nearest to the observer. For this reason'flanding paths formed by pairs of conicallyshaped equi-signal surfaces 3|, 32 and 33 are shown in full line indicating that transmitters 34, 35 and 36 are connected to radiators at the end ofthe runways 22,23 and 24 which are nearest to the observer. Separate pairs of conically-shaped equi-signal surfaces 3|', 32', and 33' may be directed from the opposite ends of runways 22. 23 and 24 by the axis of the cone.

radio beams 46 and 41. `showing the equi-signal surface 49. As shown more clearly in Fig. 4, the conically-shaped radio beams are such that their maximum radiation is in the form of a cone and al minimum amount of energy is radiated along The beam 46, is radiated along the axis 48 (Fig. 2) and the beam 41 is .radiated along substantially the same axis, but

has an apex angle smaller than that of beam 46 so its maximum radiation cone ts within that of the beam 46, This nested relation of the two beams 46 and 41 provides an over-lapping portion that forms a conically-shaped equi-signal surface 49. In the same manner, the beams 5| and 52 are arranged in nested relation about substantially the same axis 53 to over-lap in a manner such that they form the equi-signal surface 54. As shown in Figs. 5 and 6, the two conicallyshaped equi-signal surfaces 49 and 54 are arranged to define a landing path 51 by their inter-y section.. The apex angles of the radio beams are chosen to form an apex angle p for the conicallyshaped equi-signal surface that will intersect with a similar conically-shaped equi-signal surface to form a landing path inclined at any desired angle 0 with respect to the surface of the landing area. The angle 9 of the landing path may be any desired glide angle for approaching transmitters 34, and 36 connected to radiators i at said opposite ends of the respective runways. Similarly, pairs of conically-shaped equi-signal surfacesmay be radiated from opposite ends of the runways 25 26 and 21, as shown in dotted lines at 4|, 4|', 42, 42'. 43. and 43', respectivelyaircraft which is usually between 2 and 5 degrees.

In order that the intersection of the two conically-shaped equi-signal surfaces will be formed along portions of their surfaces which are inclined withrespect 'to the surface of a landing area, the axis 48 and 53 of the two cones diverge toward opposite sides of the longitudinal direction 'of the runway and hence diverge from the landing path. Preferably, the angle of. divergence is selected so the correct angle e of the landing path will be produced when tangents to the two conically-shaped equi-signalsurfaces 49 and 54.along the landing path 51 are disposed at angles of approximately 45 with respect to the surface of the landing area. The purpose of so arranging these equi-signal cones is to provide mutually perpendicular components for determining the displacement of an approaching airconically-shaped radio beams which vare arranged in nestedpairs, as shownin Fig, 2. The radiators are so arranged to emit the four beams 'from a comparatively small area which, for purposes of illustration. may be considered as contact point 45 at which aircraft land on the runr way, One pair of conicallv-shaped beams 46 and 41 arranged in nested relation about'an axis 48,

' are emitted from point 45 to form a first conica-lly-sbaped equi-signal surface 49 betweenA the two beams. A second pair of conically-shaped radio-beams 5| and 52 are emitted from the point -4'5 arranged in nested relation about an axis 53 to form a second conically-shaped equi-signal surface 54 between the two beams. The two conically-shaned equi-signal surfaces 49 and 54 in- Y slepes upwardly away from contact point 45 yas shown in Fig. 3 which is a vertical section'of the '49. Similarly, radiating wave guides 63 and 64 emit a second pair of conically-shaped radio beams such as the beams 5| and 52 to forman equi-signal cone 54.

The opposite end of the landing eld may be provided with a landing path defined by radio beams emitted from Wave guides 6|', 62263 and 64' to form corresponding conically-shaped equi-signal surfaces when it is desired to havea llanding plane approach from the opposite direction. Y

An enlarged view of lone type of radiating'wave .guide which may be used in the present invention 'is shown in Fig. 8 in which a wave guide 10 having suitable horizontal and vertical dimensions is formed with a longitudinally extending radiating slot.1| having flanges 14 extending transversely thereof. AA tapering throatfportion-12 `connects In a similar -manneryanothervantenna `II2 is.

connected to av receiverx||3 which detects radio frequency energy of a frequency F2 and supplies it simultaneously to band-pass filters I I4 and I5 that are tuned to audio frequency fr and f4. The outputs of the band-pass filters II4 and I|5 are connected to a double bridge rectifier circuit including rectier vbridges IliV and III and resistors I`|8 and I I9 that are connected to actuate pointer |2I of the cross-pointer indicator III according to the relative strengths of energy from the receiver ||3, as modulated by frequencies f3 and f4, respectively. VIn this manner, the pointerA I2| is deflected from its neutral position according to thedisplacement of the antenna ||2 witn respect tothe conicallyshaped equi-signal surface 54 formed between the two conically-shaped radio beams 5I and 52 which are modulated at frequency f3 and f4, respectively.

In operation, the air traflic control operator in thetower 29 operates remote control systems which may energize and/or deenergize solenoids |3I, |32, |33 and |34 which control the position of high frequency switches 8|, 82, 9| and 92, respectively, to direct high frequency energy from the transmitters -I5 and 85 towards one end or the otherof the runway. Similar switches are provided for Aall of the transmittingr systems and may be controlled fromthe control tower 29. Thus, depending upon conditions at the landing area, the operator may direct planes to come in from any desired direction and control the operation of the radio systems to direct beams only in thedesired direction. Obviously additional systems maybe provided for-diagonal runways as required. l

Several planes may approach the landing area at the same time and simultaneously follow parallel landing paths such as the paths dened by equi-signal surfaces 3|, 32 and 33 in Fig. 1 and follow these paths to the selected runways or landing strips 22, 23 and 24. l

Each of the landing paths is defined by the intersection of two conicallyeshaped equi-signal surfaces. Each of these surfaces is, in turn, formed by a pair of conically-shaped radio beams arranged in nested relation to overlap and form conically-shaped equi-signal surfaces. The axes of the respective cones diverge with respect to the landing area and the lapex angles of the cones are selected such that tangents to the conicallyshaped equi-signal surfaces along their line of intersection form angles of substantially 45 with respect to the horizontal and hence are mutually perpendicular.

An aircraft 'approaching a particular landing path `is provided with a pair of radio -receivers tuned to detect radio energy from the two high frequency transmitters 'I5 and 85. This detected energy is supplied to a pair of band-pass filters which pass only frequencies corresponding to a particular modulation of one of the four radio beams from the landing path. The output of Atwoband-pass filters corresponding to a, pair of beams forming the equi-signal lcone are combined and their diiference in intensity is utilized to deflect one pointer of a cross pointer meter in one direction or another depending on'which frequency is stronger. The other pointer of the cross-pointer meter is deflected in a similar manneraccording to the relative intensity of the second pair of frequencies received. Thus. the two pointers are deflected lfrom their neutral :position an amount corresponding to two component displacements of the aircraft with ,respect to the landing path .in a manner such .that the intersection of the pointer with respect to a reference point on the cross-pointer indicator'provides an indication of the displacement'of the aircraft with respect to the landing path.

As previously described, the equi-signal cones are formed by a pair of nested conically-shaped radio beams emitted from radiating wave guides that are connected to the same source of radio frequency energy; the phase velocities of waves along the guide being different to radiate conical beams having different apex angles. It' will be apparent to those skilled in the art that. if desired, the same radiating wave guides 'or a pair g of identical wave guides could be connected to sources of radio energy of different wavelengths to radiate a pair of conically-shaped 'radio beams for providing an equi-signal cone without departing from the scope of the invention.

Although the preferred embodiment of the in,- vention, as described ab'ove. deiines the landing path by the intersection of two equi-signal cones, a constant intensity type landing path maybe defined' by two conically-shaped radio beams. This may be accomplished by shutting off one of the radiators in each of the pairs, as shown in Fig. 7, to direct two conically-shaped radio beams intersecting along a line extending in the longitudinal direction of the runway. For example, radiators 6| and 63 may radiate beams 46 and 5|. These beams intersect as shown in Figs. 2 and 4, in the same vertical plane with lthe intersection of the equi-signal surfaces. By flying a path along which the energy'received from the two beams is constant and above the maximum radiation conesl an aircraft-will gradually descend to the landing area.

As is well known in constant intensity landing systems, a cross-pointer indicator may be con'- nected to a pair of receivers, thevgain of which is adjusted so, for given intensities of received signals, the pointers of the indicator are deflected to coincide with a reference mark on the face of the indicator. As the strength or intensity of the received signals increases or decreases the respective pointers are moved away from the ref.- erence position to indicate that the aircraft has deviated from the constant-intensity landing path.

When an aircraft is approaching a landing area which denes a landing path by two conicallyshaped radio beams, the gain of the receivers responding to the two conical beams may be adjusted in a conventional manner by setting the gain of the receivers at the time the craft passes over a. marker beacon and is at a specic altitude. This altitude should be selected so the aircraft is above the intersection of the cones of maximum radiation and will therefore follow a constant intensity path that is Ahigher than the intensities of the maximum radiation cones. The pilot then directs the craft to maintain the pointers at their reference lposition and in so doing keeps the craft ata position in space where ,the energy received from4 the two beams is constant. lSincethe energy radiated from the an- --tennas is more concentrated near the antennas,

the constant intensity path-.moves further from the cone of maximum radiation asV the antenna is approached. This provides a curved landing path in which the craft makes an asymptotic approach to the landing area. l I

Since many changes could be made in the above construction. and vmany apparentlyy widely different embodiments of -this inventioncould b e .radio frequency energy t form a first conically-shaped equi-signal s'urface between said beams, a second transmitter for generating radio frequency energy, and a second radiating system having radiation 'components of dissimilar transverse configuration connected to said second transmitter for emitting a pair of hollow, concave-downward, conicallyshaped radio beams arranged in nested relation to form a second conically-shaped equi-signal surface between said beams, and said latter surface intersecting said rst equi-signal surface to form a landing path.

12. -In a radio landing system, apparatus for defining a landing path comprising a first transmitter for generating radio frequency energy, a pair of cone-fire radiators having components of dissimilar transverse configuration connected to said transmitter, each of said radiators emitting Va hollow, downwardly concave conically-shaped radio beam arranged in nested relation with respect to the hollow, downwardly concave conically-shaped radio beam of the other of said radiators to form a first conically-shaped equi-signal surface, a second transmitter for generating radio frequency energy, and a second pair of cone-fire radiators having components of dissimilar transverse -conguration connected to said second transmitter, each of said last-named radiators being constructed to emit a hollow, downwardly concave conically-shaped radio beam arranged in nested relation with respect to the hollow, downwardly concave conically-shaped radio beam emitted by the other of said lastnamed radiators to form a second conicallyshaped equi-signal surface, said pairs of conelire radiators being constructed and arranged in a manner such that said conically-shaped equisignal surface intersects to form a landing path.

13. In a radio landing system, apparatus for defining a landing path comprising a pair of wave guide radiating systems having dissimilar transverse characteristics for producing a pair of hollow, downwardly concave radio beams intersecting to form a landing path, and means for supplying radio frequency energy to said radiating systems.

14. In a radio landingsystem, apparatus for defining a landing path comprising a` pair 'of wave guide radiating systemsV having dissimilar transverse characteristics for producing'a pair of conical equi-signal surfaces intersecting 'to form a landing path, and meansifor supplying to said radiating systems.

15. In a radio landing system, apparatus for defining a landing path, comprising means'for generating radio frequency energy; a/Iirst' conefire wave guide radiating system having components of dissimilar phase velocity characteristics Vconnected to said means for emittinga hollowdownwardly concave conically-shaped radio beam arranged to form a first equi-signal surface. a second cone-nre Wave guide radiating system having components of dissimilar phase velocity characteristics connected to saidmeans for emitting a second hollow, downwardly concave conically-shaped beam arranged to intersect said first conical'beam to form a landing pathextending upwardly from said radiating systems.

16. In a radio landing systemgapparatus for defining a landing path, comprising means for generating radio frequency energy', a first wave guide radiating system having components of dissimilarV phase velocity characteris'ticsv connected to said means for emittine'a pair of radio bearns arranged to form a first equi-signal surface, v'a second wave guide'radiating system havingr components of dissimilar phase velocity character-'- istics connected to said means for emitting a second pair of radio beams arranged to form a second equi-signal surface intersecting saidV first equi-signal surface to form a landing path extending upwardly from said radiating systems.

17. In a radio landing system, apparatus for defining a landing path, comprising means for generating radio frequency energy of a selected wavelength, a first pair of cone-fire radiating wave guides constructed to provide different phase velocities for energy of said wavelength connected to said wave guides for emitting a pair of nested conically-shaped radio beams to form a first conically-shaped equi-signal surface. means for generating radio frequency energy of a second selected wavelength, and a pair of conere radiating waveguides constructed to provide different phase velocities for said selected'wave'- lengths connected to said Wave guides for emitting a pair of conically-shaped radio beams to form a second conically-shaped equi-signal surface, said cone-fire radiating wave guides being arranged in a manner such that said equi-signal surfaces intersect to form a landing path.;I

18. In a landing system for a landingfarea, apparatus for defining a landing path compris'- ing a first antenna system arranged substantially flush with the surface of said'landing area for radiating a curved beam of electromagnetic energy at an angle with said area substantially of the same order of magnitude as the angle of said landing pathand curving upwardly from said landizzgarea in one direction and extending in the general longitudinal direction of a runway, and a second similarly constructed antenna system for radiating a curved beam of electromagnetic energy at the aforesaid rangle curving upwardly toward said first .beam in the opposite direction thereto and extending inthe general longitudina1 direction of said runway, said antennarsystems being arranged ina manner such that the intersection `of said beams forms a landing path projecting upwardly from and in the longitudinal direction of said runway. 19. In a landing system for a landing area, apparatus for defining a landing path comprising a rst antenna system arranged substantially A,flush with said landing area radiating a` nested pair of curved beams of electromagnetic energy arranged at anangle substantially of the same order of magnitude as the angle of said landing path to form afirst equi-signal surface curving upwardly from Aa landing area in one direction and extending in the general longitudinaldirection of a runway, and a second antenna system similarly constructed radiating a nested pair of curved beams of electromagnetic energy at the 'aforesaid angle to form a second equi-signal surface curving upwardly toward said first' equisignal surface in the opposite direction thereto and extending in the general longitudinal direction of said runway, said antenna systems being arranged in a manner vsuch that the intersection of said equi-signal surfaces forms a landing path projecting upwardly'from and inthe longitudina1 direction of said runway.

20. In a landingY system for a landing area, apparatus for-defining a llanding path comprising a first antenna system arranged substantiallyfiiush with said landing arearadiating a nested pair of hollow conically-shaped beams-'of terrasse ila amanner such that said'ia'xes vergeianki said arranged anutanother axisto fformJan-fequiisigtialsurfacelcurved symmetrically Aabout fsaid "ot'hrxis "substantially i parallel to 'jsaid `jlandirig area anu extending-fin i the Jgeneral longitudinal directicnf saidrunway said "antenna systems tin' having radiator components of dissimilar' phase velocity-fcharacteristicsfor producing a conically-shaped equi-signal surface having its axisieiterlingsubstantially iparallelitof and in the general longitudinal directioniifflarunway, but diverging'therefrom, andra Vwsecond antenna system having radiator components of dissimi- 4lar phase velocity characteristics for producing :a fseeifu `ezmicany:sinpeu d'equiesignal surface Iiyitig its laxis extending sub'sftantially parallel to` arid i'nitli'e"generalu longitudinal direction *of said runway, but diverging from said runway in a direction opposite to the axis of said first equisignal surface, said antenna systems being arranged in a manner such that said equi-signal surfaces intersect to form a landing path pro- 75 ai@ `about 'an YEa jieiigitudin no suenan "tnnasystems lbeingarrangedfi '50 @nase*velocity =eliarafcteristiesMcorinectedf-to"said nal surface between said beams.

28. In a radio landing system for a landing area, apparatus comprising means for generating radio frequency energy, means coupling said generating means to a plurality of cone-fire radiators vguide radiators arranged substantially flush lwith the surfaceof said landing area, eachwave guide of a guide pair having a transverse'conguration Adiffering from the other guide of said same `guide pair, to radiate nested pairs of hemifconically shaped radio beams, said beams having conical equi-signal -surfaces residing therebetween, and having an angle with said landing area in Vthe sameorder of magnitude as the Vlanding angle of the landing'pathv formed by the intersection of a pair of said equi-signal surfaces. Y Y .Y

30. In a radio llanding system fora landing area, apparatus comprising means for generating radio frequency energy, meansA coupling said gen- Verating .means to two pairsof aperturedvwave guide radiators arranged substantially flush with the surface of said landing area,- each wave-guide of `a guide pair having dissimilar phase velocity vcharacteristics diering from the other guideof said same guide pair, to radiate nested jpairs of hemi-conically shapedY radio beams, said'beams having conical lequi-signal surfaces residing therebetween, andV having an VangleY withv said landing areainthe sameorderofmaglnitude as .the landing angle of the landingwpat'l formed by .the intersection of a pair of said-equi-signalsurvfaces;4

. 31..'1n a radiov musing system 'fer La landing area-,apparatus comprising-means for generating radio frequency energy, means coupling said generating means to a plurality Aof wave guide radiators.arrangedsubstantially flushwith the surface of said landing area, said radiatorsfhaving dissimilar phase Velocity characteristics and radiating A'substantially conically-shaped radio beams into space about an axis coincidentc'with the longitudinal axis of saidfwavev guidesfsaid beams intersecting to define a landing path-for approaching said landing area.V r

V32. In .asystem for landing an'arcraft, the method which comprises forming a-pair offinter'- vsecting conical equi-signal surfaces and directing Saidair'craft vertically and horizontally along ya landing path determined by the intersectionof said surfaces.

'33. In a system for landing an a craft,the

method which comprisesforming'aplurality of directive radio beams substantially inthe shape of vhollow cones having apexes substantially' on the ground, placing the beams in nested relation to produce equifsignal conical surfaces therebetween, intersecting said surfaces and directing lsaid aircraft transverse to said landing areaalong a landing path determined bythe intersection of said equi-signal surfaces.

34.1ri a system for landing an aircraft', the

method which comprises forming a plurality of directive radio beams substantially inthe shape of hollow hemi-cones, placing said rbeams in nested relation to produce equi-signal conical vlanding path determined by the intersection of said equi-signal surfaces.

36. In a system forv landing an aircraft.- the method which comprises forming a plurality of directive radio beams substantially in the shape of hollow conical sections, said sections being concaved downwards, placing said beams in nestedy relation to produce equi-signal surfaces therebetween, intersecting saidA equi-signal surfaces and. directing said aircraft transversely to a landing area along a landing path determined by the intersection of said surfaces.- Y

37. In a system for landing an aircraft, the method which comprises forming a plurality of directive radio-beams*substantially.in the shape of hollow cones having apexes substantially on the ground, placing said Abeams in nested relation to produce equi-signal surfaces therebetween, in*- tersecting said equi-signal surfaces, and directing said aircraft vertically and horizontally along a landing path formed thereby and having a landing angle substantially .of the same order ofv magnitude as the apex angle of said conical beams. 38; In a system for-landing an -aircraft -in a, .landing area, the method which comprises forming a plurality of directive radio beams substantially in the shape of vhollow cones having vaxes of revolution substantially parallel to said land.- ing area, placing said beams` in nested relation to produce equi-signal surfaces therebetween, intersecting said equi-signal surfaces and directing .said aircraft verticallyand horizontally along a landing path determined by the intersection of said surfaces.

39. 'in a system'for .landing an aircraft in' a landing area, the method which comprises formto produce equi-signal surfaces therebetween, in-

tersecting saidequi-signal surfaces and directing saidaircraft transversely to a landing area along a landing path formed thereby and having a landing angle substantially 'of the same order of magnitude as vthe apex angle of said conical beams.

v RUSSELL H. VARIAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,120,241 Diamond et al. June 14, 1938 2,165,256 Hansell July 11, 1939 2,294,882 Alford Sept. 8, 1942 d 

